Circuit Description

PCM monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this period, PCM counts the number of Lean/Rich (L/R) and Rich/Lean (R/L) switches. With this information, an average time for all transitions can be determined. PCM then divides R/L average by L/R rich average to obtain a ratio. If HO2S ratio is not within range, DTC will set.

Conditions for setting DTC are: PCM detects that bank 1, sensor 1 transition time ratio is less than 0.4 and greater than 4 and condition is present for 2 minutes after "closed-loop" enable.